The disclosure of Japanese Patent Application No. HEI 10-232875 filed on Aug. 19, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The present invention relates to a catalyst deterioration detector that detects the deterioration of a catalytic device for purifying noxious substances contained in exhaust gas in an internal combustion engine. The present invention also relates to a method of detecting the deterioration of a catalytic device.
2. Description of Related Art
Exhaust gas discharged from an internal combustion engine such as a gasoline engine contains noxious substances (exhaust emission substances) including hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (NOx). In order to purify these noxious substances by oxidation or reduction, catalytic devices are disposed in an exhaust passage through which the exhaust gas flows. As a result of deterioration in quality, these catalytic devices reduce their capacities to purify the noxious substances. Therefore, various measures have been taken to detect deterioration of the catalytic devices. For example, Japanese Laid-Open Patent Application No. HEI 9-32535 discloses an exemplary catalyst deterioration detector.
Due to the improved understanding and enforcement of environmental protection in recent years, it has been required to further reduce concentrations of exhaust emission substances. For this reason, the present inventors have been focusing attention on the adsorbing function of catalysts, as well as the oxidizing and reducing functions that are intrinsically attributed to catalysts, in order to further reduce concentrations of exhaust emission substances. Accordingly, there is a need for a detector capable of detecting deterioration in the adsorbing function of catalysts. However, known detectors such as the deterioration detector disclosed in Japanese Laid-Open Patent Application No. HEI 9-32535 are mainly intended to detect deterioration in the oxidizing and reducing functions of catalysts, and not to detect deterioration in the adsorbing function.
It is an object of the present invention to provide a catalyst deterioration detector that detects the deterioration of a catalytic device, particularly deterioration in the adsorbing function of the catalytic device.
An aspect of the present invention provides a catalyst deterioration detector for use with a first catalytic device that is disposed in an exhaust passage of an internal combustion engine. The first catalytic device includes a first catalyst and adsorbs hydrocarbons and oxidizes the hydrocarbons at a temperature equal to or higher than an activation temperature of the first catalytic device. The catalyst deterioration detector comprises an adsorption detector that detects a degree of adsorption of hydrocarbons by the first catalytic device, and a controller that determines the deterioration of the catalytic device according to the degree of adsorption detected by the adsorption detector.
In this aspect of the invention, the degree of adsorption of hydrocarbons by the first catalytic device is detected. If the detected degree of adsorption is smaller than a certain level, the controller determines that the adsorbing function of the first catalytic device has deteriorated. As a result, it is possible to precisely detect deterioration in adsorbing function of the first catalytic device.
Furthermore, in certain embodiments of the present invention, the adsorption detector can be disposed in the exhaust passage downstream of the first catalytic device. In such embodiments, the adsorption detector can be a detector that detects an amount of hydrocarbon discharged from the first catalytic device. Thereby, it is possible to determine a degree of adsorption of hydrocarbons by the first catalytic device by detecting an amount of hydrocarbons downstream of the first catalytic device. Such embodiments utilize the fact that when the degree of adsorption of hydrocarbons by the first catalytic device is at a low level, the amount of hydrocarbons that flows out toward the downstream side of the first catalytic device increases. Thus, there is no need to directly detect an amount of hydrocarbons adsorbed by the first catalytic device, and the degree of hydrocarbon adsorption of the first catalytic device can be detected using exhaust gas downstream of the first catalytic device. Therefore, the degree of adsorption can be determined easily.
Furthermore, the hydrocarbon detector can include a detection-oriented, second catalytic device that includes a second catalyst and oxidizes hydrocarbons, and a temperature detector that detects a temperature of the second catalytic device. In such embodiments, the hydrocarbons that flow out toward the downstream side of the first catalytic device are oxidized using the second catalytic device, and the temperature detector detects a change in temperature resulting from oxidation heat generated during this oxidation. In this manner, the degree of adsorption of the hydrocarbons can be detected. The hydrocarbon detector can comprise a second catalytic device and a temperature detector, such as a temperature sensor. The hydrocarbon detector can easily be mounted in the exhaust passage. Furthermore, it is possible not only to detect deterioration in the adsorbing function of the first catalytic device, but also to purify exhaust gas by oxidation of hydrocarbons by the second catalytic device.
Furthermore, the second catalytic device can be a heat-up type catalytic device, that is electrically activated to generate heat or to heat up. Thereby, the second catalytic device can be heated up and brought to its activation temperature at an early stage of engine operation. Thus, it is possible to detect more precisely a degree of deterioration in the adsorbing function of the first catalytic device. Also, because the second catalytic device reaches its activation temperature at an earlier stage, it is possible not only to detect a degree of deterioration in the adsorbing function of the first catalytic device, but also to oxidize hydrocarbons at an earlier stage of engine operation. Consequently, the purification of hydrocarbons can be achieved at an earlier stage of engine operation.